(a) Field of Disclosure
The present disclosure of invention relates to display devices. More particularly, the present disclosure relates to a liquid crystal display (LCD) capable of displaying images at different viewing angles by using light transmittance through a polarizing liquid crystal material layer.
(b) Description of Related Technology
A typical liquid crystal display includes a liquid crystal panel displaying images by using light provided from a backlighting assembly disposed under the liquid crystal panel where the provided light is polarized in one direction when provided from underneath toward and through the liquid crystal panel and where the liquid crystal panel can modify the polarization of the light and thereby modulate the passed through luminance.
The liquid crystal panel includes a first substrate having a plurality of thin film transistors (TFT's) each coupled to a respective pixel electrode, a second substrate spaced apart from but facing the first substrate and having a common electrode thereon, and a light-polarizing liquid crystal material layer interposed between the first substrate and the second substrate.
The liquid crystals in the liquid crystal layer may be structured to operate in a vertical alignment mode (VAM). Their light polarizing effects may be modulated by use of an electric field formed between a given pixel electrode (of a given pixel) and the correspondingly spaced apart portion of the common electrode. For example, if an electric field is not generated between the pixel electrode and the common electrode (a zero field magnitude), the VAM liquid crystal location may appear as a black image (maximally darkened pixel) due to the way that polarized light is processed by various layers of the LCD panel including by the VAM liquid crystal layer. On the other hand, when an electric field of nonzero and varying magnitude is generated between the pixel electrode and the common electrode, images of several corresponding grays may be presented to a viewer who is facing the screen square on (so that viewed light rays leave the screen at right angles to the screen surface).
When increasing magnitudes of electric field intensity are generated between the pixel electrode and the common electrode, corresponding images that are gradually brighter and brighter are realized. This occurs because the VAM liquid crystals in the liquid crystal layer are becoming aligned to be more parallel to the substrates and their VA mode of operation then lets more and more light through (due to polarization effects) as the angles of the crystals with respect to the pixel electrode or the common electrode shift further and further away from the fully relaxed 90 degrees. On the other hand, when the VAM liquid crystals are arranged in the vertical direction (to be relaxed at 90 degrees relative to the substrate surfaces), an excellent black image having relatively low luminance is displayed to a person viewing the front side of the liquid crystal panel head on (so that viewed light rays emerge from the panel at 90 degree angles relative to the substrate surfaces). However, for a person viewing the front side of the liquid crystal panel at an angle (from a side of the display rather than head on), the pixels which are supposed to have a maximally black imagery instead appear with undesirably higher luminances (e.g., gray rather than black). This happens because the light rays progressing towards the side view direction of the liquid crystal panel pass obliquely rather than square on through the liquid crystal material layer and these obliquely passing through light rays experience a larger phase retardation effect (R, which may be measured in nanometers) resulting from the greater thickness of, and the differently tilted relative angles of the liquid crystals the light rays pass through as compared to the light rays that progress normally in the head-on, front direction of the panel through the liquid crystal material layer.
As described above, in the liquid crystal panel that is operated in the conventional vertical alignment mode (VAM) and having no compensation for oblique light rays, the side-viewed luminances of pixels that are supposed to be fully black image are observed to be higher than desired and the brightness contrast ratio is thus decreased for persons viewing the panel from a side angle rather than head-on.
The above information disclosed in this Background section is only for enhancement of understanding of the background and of the technology of what is disclosed here and therefore the Background information it may contain information that does not form part of the prior art that is already known to persons of ordinary skill in the pertinent art.